Generally, a refrigerator includes a main body having an inner casing and an outer casing, a storage chamber formed by the inner space, and a cool air supply device to supply cool air to the storage chamber, to thereby store foods in a fresh state.
A temperature of the storage chamber is maintained within a predetermined range needed to store foods in a fresh state.
The storage chamber of the refrigerator has an opened front surface, and the opened front surface is closed by a door in such a manner that a temperature of the storage chamber is properly maintained at ordinary times.
The insulation is foamed between the inner casing and the outer casing of the main body so as to prevent leakage of cool air from the storage chamber.
Since the insulation is foamed at a predetermined temperature or higher, heat occurs in the insulation foaming process, a temperature of the main body may be higher than a room temperature (or normal temperature) by about 20° C. or higher on the condition that the insulation is foamed between the inner casing and the outer casing.
After the insulation is foamed between the inner casing and the outer casing, as a temperature of the main body gradually drops to a room (or normal) temperature, the insulation is hardened or stiffened, and the main body is thermally contracted.
The inner casing may be generally formed of a plastic material, and the outer casing may be generally formed of steel. The degree of thermal contraction of the plastic material may be higher than that of the steel material by about 5 times or higher. As a result, when the main body is thermally contracted, the inner casing is thermally contracted much more than the outer casing. Thus, during a predetermined time in which the temperature of the main body drops to room temperature, the center part of both sides of the main body is modified into a convex shape in an outward direction of the main body. Under the condition that the temperature of the main body drops to the room temperature, the center part of both sides of the main body is modified into a convex shape in an outward direction of the main body such that the insulation is hardened or stiffened.
When deformation occurs in the inner casing and the outer casing due to a difference in thermal contraction between the inner casing and the outer casing, such deformation of the inner casing and the outer casing may be regularly reduced by the insulation contacting each of the inner casing and the outer casing. If thickness of the insulation foamed between the inner casing and the outer casing is reduced so as to implement the same exterior size as well as to increase inner capacity (or inner volume) of the main body, the degree of deformation in which the center part of both sides of the main body is modified into a convex shape in an outward direction of the main body may unavoidably increase. When a refrigerator starts operation upon completion of insulation foam, the internal temperature of the main body is lowered and at the same time the degree of thermal contraction of the inner casing is increased, resulting in an increase in the degree of deformation of the exterior shape.
In addition, if thickness of the insulation is reduced, insulation performance may be deteriorated. Stiffness or rigidity of the inner casing and the outer casing is weakened, such that the main body may be modified in shape not only by a weight of the main body but also by a weight of materials stored in the main body.
In order to improve deteriorated insulation performance caused by a reduced thickness of the insulation, not only the insulation but also a vacuum insulation may be disposed between the inner casing and the outer casing. However, although the vacuum insulation and the insulation are disposed between the inner casing and the outer casing, it is impossible to reinforce weakened stiffness whereas insulation performance is improved.